1. Field of the Invention
This invention relates generally to catheters. More specifically, the present invention relates to a method of attaching a catheter hub to the end of a catheter tube, and an improvement in strain relief therebetween.
2. Prior Art
Medical catheters generally comprise a flexible catheter tube which is permanently attached at one end to a rigid hub. The hub functions as a connector to allow quick connection of a syringe or the like to the catheter. Because bending forces applied to the catheter tube tend to be concentrate at the hub/catheter tube juncture, a strain relief is usually incorporated into the hub/catheter tube juncture to help avoid collapse of the catheter tube due to these periodic force concentrations which occur during use.
Strain relief devices are traditionally formed of a material which is more flexible than the hub and less flexible than the catheter tube. The strain relief device is generally formed of a sufficient length to allow attachment of one end thereof to the hub while allowing the opposite end to extend a substantial distance along the catheter tube beyond the hub/catheter tube juncture. With such a strain relief device in place, bending forces applied to the tube at the juncture area are resisted by the strain relief device and prevented from concentrating sufficiently at the juncture to cause collapse of the catheter tube. The strain relief device thereby functions to "relieve" the strain at the juncture by spreading bending forces along a larger length of the catheter tube.
Although strain relief devices of this type have in the past functioned adequately to relief the strain of bending forces at a hub/catheter tube juncture, they have nevertheless failed to aid in strengthening the juncture against axial forces, i.e., forces along the longitudinal axis of the catheter tube which tend to pull the catheter tube away from the hub nor significantly aided in forming or strengthening the hub/catheter tube attachment itself. Longitudinal ("pulling") forces can arise during the use of a catheter through any number of commonly occurring accidents or mishaps, and can lead to disastrous consequences for a patient who may heavily rely on the proper functioning of the catheter.
For example, serious if not fatal consequences can result from incidental hub/catheter tube separation when the catheter is in use in a patient, especially when the catheter is placed within an artery or vein. A release of the catheter tube subsequent to separation from its hub can actually resulted in the catheter tube becoming lost in the patient's cardiovascular system. Alternatively, the incidental separation of a catheter tube from its hub, if gone unnoticed, may prevent the infusion of important medicaments or other fluids into a patient. Obviously, in each instance the results can be disastrous for the patient.
A major manufacturing problem occurring with prior art catheters which makes it difficult to form a strain relief which can also inhibit separation due to pulling forces as well as prevent kinking due to bending forces includes the difficulty in securely attaching the relatively flexible catheter tube of a particular polymeric material to the relatively rigid hub of different polymeric material in a secure manner. Secure catheter tube/hub attachment is especially problematic since many polymeric materials are incompatible for secure and reliable attachment by adhesive, solvent, heat, or other chemical bonding. It can be necessary therefore to attach the catheter tube to the hub by means of a mechanical attachment, which is apart from and in addition to the strain relief, and which functions independently of the strain relief to inhibit separation due to pulling forces.
Czuba et al., U.S. Pat. No. 4,391,029, is exemplary of prior art catheter assemblies which include the attachment of a catheter tube to a hub by means of a mechanical attachment which is separate and in addition to the strain relief. Czuba et al.'s catheter includes a catheter tube end which is enlarged relative to the remainder of the catheter tube, and which is sized to fit within the hub. A rigid tubular funnel is inserted into the lumen of the catheter tube to prevent any subsequent collapse and/or passage of the enlarged end of the catheter tube through the relatively constricted portion of the hub should there be an attempt to pull the catheter out of the hub. As can be seen in the Czuba et al. patent, the strain relief of the Czuba et al. device is completely separate from the enlarged end of the catheter tube and the rigid tubular funnel.
Prior art catheter/hub connection methods such as described in Czuba et al. above, while functioning well to prevent inadvertent separation of the catheter tube and hub, nevertheless are somewhat difficult to manufacture and relatively expensive due to the added elements and materials used, and due to the manufacturing procedures necessitated thereby.
There therefore exists a need in the art to develop a catheter having a catheter tube/hub connection which is inexpensive in materials and manufacturing, and which can secure the connection therebetween regardless of the materials composing the catheter tube or the hub, in a secure inseparable relationship. Further, there exists a need in the art to develop a strain relief between a catheter tube and hub which can function both to prevent inadvertent kinking or bending of the catheter tube while in use, and to inhibit separation due to applied longitudinal pulling forces.